A number of diseases, illnesses and other medical conditions are treatable at least in part by dilatation of a bone, tissue or duct. For example, medical conditions and/or physical injuries can lead to or predispose a bone to deformity, such as a fracture. A familiar example is osteoporosis, in which bones lose calcium and break more easily. The human spinal column, comprised of interconnected vertebrae or vertebral bodies, has proven to be especially susceptible to the effects of osteoporosis. A vertebral body weakened by osteoporosis can fracture from a fall, or simply during routine activities. When a vertebral body fractures, it can collapse and change the shape of the spine. The damaged portion of the spine becomes shorter, and the rest of the spine above the broken vertebral body bends forward. As additional vertebral fractures occur, the spine shortens further, increasingly forcing the individual into a hunched-over posture.
As taught by U.S. Pat. No. 6,248,110 (Reiley et al.), U.S. Pat. No. 6,235,043 (Reiley et al.) and U.S. Pat. No. 6,066,154 (Reiley et al.), each of which is incorporated herein in its entirety by reference, it is known in the art to use expandable bodies, such as a balloon element, to treat certain bone conditions, resulting from osteoporosis, avascular necrosis, bone cancer and the like, that predispose a bone to, or lead to, fracture or collapse. A particularly common application is in the treatment of vertebral body compression fractures resulting from osteoporosis.
Typical treatment of such conditions includes a series of steps which a surgeon or health care provider can perform to form a cavity in an interior region of pathological bone, including but not limited to osteoporotic bone, osteoporotic fractured metaphyseal and epiphyseal bone, osteoporotic vertebral bodies, fractured osteoporotic vertebral bodies, fractures of vertebral bodies due to tumors especially round cell tumors, avascular necrosis of the epiphyses of long bones, especially avascular necrosis of the proximal femur, distal femur and proximal humerus and defects arising from endocrine conditions.
The method typically further includes the steps of making an incision in the skin (usually one incision, but a second small incision may also be required if a suction egress is used) followed by the placement of a guide pin which is passed through the soft tissue down to and into the bone.
The method of the Reiley '154 patent, for example, further includes the steps of drilling the bone to be treated to form a cavity or passage in the bone, following which an inflatable balloon-like device is inserted into the cavity or passage where it is inflated. The inflation of the inflatable device causes a compacting of the cancellous bone and bone marrow against the inner surface of the cortical wall of the bone to further enlarge the cavity or passage. The inflatable device is then deflated and then is completely removed from the bone. The art further teaches that a smaller inflatable device (a starter balloon) can be used initially, if needed, to initiate the compacting of the bone marrow and to commence the formation of the cavity or passage in the cancellous bone and marrow. After this has occurred, a larger, inflatable device can be inserted into the cavity or passage to further compact the bone marrow in all directions.
Next in accordance with Reiley '154, a flowable biocompatible filling material, such as methylmethacrylate cement or a synthetic bone substitute, is directed into the bone cavity or passage that has been formed and enlarged, and the filling material is allowed to set to a hardened condition to provide ongoing structural support for the bone. Following this latter step, the insertion instruments are removed from the body and the incision in the skin is covered with a bandage.
A related U.S. Pat. No. 6,048,346 (Reiley et al.), which is also incorporated herein in its entirety by reference, teaches an improved mechanical bone cement injection assembly, which is described as constituting an improvement over prior art devices that operated “similar to a household caulking gun” in that it facilitates greater control over the placement of cement and other flowable liquids into an interior region of a bone.
Another inflatable apparatus intended for deployment into interior body regions is described in U.S. Pat. No. 5,972,015 (Scribner et al.), which is also incorporated herein in its entirety by reference. The Scribner '015 patent describes a catheter tube extending along a first axis in conjunction with an expandable structure having an expanded geometry oriented about a second axis, not aligned with the first axis, so as to treat an asymmetrically-shaped interior body region or where the access channel cannot be aligned with the body region to be treated. A particular application of this technology is stated to be for the fixation of fractures or other osteoporotic and non-osteoporotic conditions of human and animal bones, specifically for treating a human lumbar vertebra.
Two somewhat earlier patents describing similar apparatus and methods for treating vertebral body compression fractures and the like using an inflatable balloon-like element inserted into the bone cavity are U.S. Pat. No. 5,108,404 (Scholten et al.) and U.S. Pat. No. 4,969,888 (Scholten et al.), each of which is also incorporated herein in its entirety by reference.
In additional embodiments of known technologies for treating bone structures, U.S. Pat. No. 6,613,054 (Scribner et al.) and U.S. Pat. No. 6,241,734 (Scribner et al.), each of which is incorporated herein in its entirety by reference, describe systems and methods for advancing a tamping instrument through a cannula that has been deployed to establish a subcutaneous channel into bone. Material is introduced into the bone through the cannula, and the tamping instrument is used to move material in the cannula into the bone.
Numerous problems remain, however, with the prior art systems and methods. For successful expansion of a fractured vertebral body, an expandable element inserted into the vertebral cavity must be capable of being inflated to a relatively large working diameter of about 12 mm-25 mm, starting with a relatively short balloon working length, e.g., about 10 mm-25 mm, sized to fit inside the vertebral cavity, at very high working pressures on the order of 200-450 psi or higher. Use of lower inflation pressure in such applications may result in only a partial, incomplete expansion of a fractured vertebral body. When that partially-expanded vertebral body is subsequently filled with cement or comparable material, which then hardens, there is a permanent remaining spinal deformity at that vertebral body. Not only must the expandable/inflatable element in the vertebral cavity be capable of inflation to very high pressure without rupture in order to fully expand a collapsed/fractured vertebral body, in addition the inflated element must resist puncture by hard, sharp cancellous bone and surface irregularities around the outer edges of the vertebral cavity.
One possible approach to improve the strength of the balloon-like elements to make them better able to withstand very high inflation pressures would be to use thicker balloon walls and/or to make these elements out of stiffer, stronger materials. There are several reasons, however, why these seemingly straightforward solutions have not proven successful in practice. One is the need to limit the balloon wall thickness and the need to maintain balloon wall flexibility to facilitate access to, and withdrawal from, a bone cavity.
In treating a vertebral fracture, for example, the vertebral cavity is typically accessed by drilling a small hole and locating a short, hollow, metallic tubular element (i.e., a hollow sleeve or cannula) through the left or right pedicle portion (or sometimes both) of the vertebral arch (see, e.g., FIG. 2 of U.S. Pat. No. 5,972,015, which shows the left and right pedicle portions 42 of vertebral arch 40, and FIG. 6 of the same patent which shows an access hole for catheter tube 50 and expandable structure 56 through one pedicle portion 42 into the interior volume 30 of reticulated cancellous, or spongy, bone 32). Because pedicle portion 42 shown in FIGS. 2 and 6 of the Scribner '015 patent is relatively small and is itself readily susceptible to fracture if its structural integrity is impaired by too large a hole, it is crucial to keep the diameter of the hole, therefore also of the cannula, to a minimum, typically no larger than about 4-5 mm. Indeed, as taught hereinafter, it has become desirable based on current medical practice to use an opening made by an 11-gauge needle with a diameter of only about 0.121 inches (about 3.06 mm) or less, thereby requiring the use of an 11-gauge needle cannula. The cannula helps to protect surrounding bone portions from abrasion and from expansion forces while inserting or removing the catheter shaft or while inflating the balloon element that is bonded to the distal end of the catheter shaft.
Because of the narrow interior diameter of the cannula used in these applications, it was typical to fold or wrap the balloon-like element relatively tightly at the distal end of an associated catheter shaft in order to keep the maximum diameter of the unit at the balloon end small enough to fit through the cannula of a small-diameter pedicle hole. An expandable element fabricated with relatively thick walls and/or made from a relatively stiff, less flexible material might be inflatable to a higher pressure, but these characteristics could impede folding or wrapping the element tightly enough to fit through the cannula of a narrow-diameter pedicle opening. For these reasons, balloon elements for bone dilatation procedures would typically have thicker walls compared, for example, to the balloon elements commonly used for angioplasty procedures, but the bone dilatation balloons would generally be fabricated from more flexible, elastic materials than those used in angioplasty procedures.
Even if a balloon element can be wrapped or folded sufficiently tightly for insertion through the cannula of a narrow-diameter pedicle hole, it can later be difficult to remove or withdraw that balloon element through the same cannula following a dilatation procedure because, after a cycle of inflation and deflation inside a vertebral cavity, a balloon element may not be able to be refolded or rewrapped in-situ to its previously folded size or to a size sufficiently small to be withdrawn through the cannula without the use of excessive force which might crack or break the pedicle or tear the balloon from the catheter.
These problems were addressed, at least in part, by U.S. Pat. No. 7,488,337 (Saab et al.), which is incorporated herein in its entirety by reference. Saab '337 describes techniques for tensioning, stretching, folding and/or wrapping the expandable elements of devices designed for bone dilatation procedures to better facilitate insertion of the expandable elements into and, after an inflation procedure, withdrawal of the expandable elements from a bone structure through a narrow diameter cannula.
As noted above, however, the trend in medical practice in this field has been to utilize the smallest possible diameter hole or holes through the exterior portion of the bone to access the bone interior region. Current practice is to use an 11-gauge needle in order to perform a vertebral treatment, if possible, using bone openings that are so small (about 0.120 inches) that they can only accommodate an eleven (11) gauge cannula. Currently available catheter/expandable element apparatus for such bone treatment procedures, however, cannot be inserted into or withdrawn from a bone dilatation site through a standard wall 11-gauge cannula (which typically has an inside diameter of only 0.094 inches±0.002 inches). By contrast with an 11-gauge cannula, a thin-walled 10-gauge needle cannula (having a thinner wall thickness than a “standard” 10G cannula), which has become the industry standard for Kyphoplasty procedures, has an inside diameter of 0.114 inches (2.89 mm) The thin-walled 10-gauge cannula and its 0.114 inch inside diameter can accommodate current catheter assemblies used in these procedures, but it also has a larger outside diameter of about 0.134 inches that cannot fit inside a bone opening of only about 0.121 inches, which is the size of the opening made with an 11-gauge needle.
But, adapting the technology in this field to a smaller 11-gauge cannula, having an inside diameter (ID) of about 0.094 inches (2.39 mm)±0.002 inches and an outside diameter (OD) of about 0.120 inches (3.05 mm)±0.001 inches involves many substantial technological challenges. Much more is involved in this adaptation than just slightly shrinking all of the standard apparatus components.
First, because the volume of the bone interior that needs expanding remains unchanged, the expandable element must still be capable of expanding to that necessary bone interior volume, but that expandable element also needs to fit through the smaller interior diameter of an 11-gauge cannula. One approach to facilitate the insertion and removal steps with the larger, conventional 8-gauge and 10-gauge cannulas is to provide a slippery, friction-reducing coating or lubricating fluid (such as a silicone material) along the interior of the cannula, on the exterior of the expandable element, or both, to reduce friction and facilitate sliding the expandable element through the cannula.
A potential problem with this lubricant coating approach, however, is that at least a portion of such a lubricant would be transferred via the expandable element into the interior of the bone, where it would remain as a foreign contaminant. The presence of such a contaminant might cause irritation or an adverse body reaction at the interior bone site. In addition, the presence of a lubricating substance coating the walls of the expanded cavity of the bone following a dilatation procedure can possibly prevent a subsequently injected cement material from solidly and effectively bonding to the bone interior.
It also is not currently feasible to facilitate the use of an 11-gauge cannula in these procedures by reducing the wall thickness of the expandable element. As discussed above, the expandable element needs to withstand inflation to relatively high pressure without being punctured by irregularities or projecting portions of the bone interior. Furthermore, current medical protocols for bone dilatation procedures using an expandable balloon prescribe the minimum acceptable wall thickness for the expandable element, and those protocols must be met whether the balloon element needs to fit through the interior of a conventional 8-gauge or 10-gauge cannula, or through a very narrow diameter 11-gauge cannula.
Structural integrity and materials issues for the cannula create another significant design constraint. A “standard” 11-gauge cannula has an interior diameter (ID) of 0.094 inches with a tolerance of ±0.002 inches (i.e., an interior diameter that may range from 0.092 to 0.096 inches) and an outer diameter (OD) ranging from 0.119 to 0.121 inches (about 3.05 mm) In theory, one could make an ultra-thin walled 11-gauge cannula with an interior diameter of about 0.114 inches (i.e., comparable to a thin-walled 10-gauge cannula) but with a very thin wall such that the outer diameter was only about 0.120 inches. But, such an ultra-thin wall of only about 0.003 inches would compromise the structural integrity of the cannula which must function under demanding operating conditions. Such a modification would therefore raise numerous patient safety issues.
Another performance issue in this field is being able to accurately monitor the location of the expandable element as it is slid through the cannula and into the interior region of the bone that is being treated. This is an important issue because the length (along the catheter axis) of the expandable element (before inflation) is carefully selected to correspond to the size of the bone interior when the element is fully inflated.
Because of these narrow tolerances, it is important that the expandable element be properly situated in the bone interior before an inflation procedure is initiated. If the expandable element is pushed too hard and too far into the bone interior region, the distal tip of the catheter/expandable element may damage or even rupture the distal wall of the bone interior region. On the other hand, if the proximal portion of the expandable element is still located inside the cannula when the inflation procedure is started, the expandable element will be unable to fully inflate and, thus, unable to fully dilate the bone interior.
One approach to addressing the expandable element positioning problem has been to place radiopaque markings at one or more locations inside the expandable element and, using appropriate fluoroscopy equipment, to monitor the location of the expandable element by means of those markings as it is slid through the cannula and into the interior of the bone structure. Although the thickness of such radiopaque markings is generally very small, even that small added thickness becomes a significant factor in the context of wrapping or folding a full-sized bone dilatation expandable element to fit through the very small inside diameter of an 11-gauge cannula.
Yet another factor that becomes significant in the context of fitting a full-sized bone dilatation expandable element through the interior of an 11-gauge cannula is the juncture where the proximal end of the expandable element is secured to the distal end of the catheter shaft on which the expandable element is carried. Typically, the opening at the proximal end of the expandable element is formed slightly larger than the exterior diameter of the distal end of the catheter shaft. Thus, the proximal end of the expandable element can be slid over the distal end of the catheter shaft, and the expandable element can then be sealed to the end of the shaft by gluing, thermal bonding, or using similar sealing techniques. The result of this bonding procedure, however, is typically a small section of enlarged diameter at the juncture between the two components, and such an enlarged diameter section of the combined apparatus can inhibit passage of the expandable element through the interior of an 11-gauge cannula.
Still another design constraint of conventional expandable element bone dilatation systems is the use of a catheter shaft having an annular configuration with concentric inner and outer lumens. This coaxial, dual-lumen structure permits the outer lumen to be used for flowing a fluid (such as air, water or contrast fluid) to or from the expandable element for inflating or deflating the element once it is in place inside the bone, while using the separate inner lumen (which extends to the interior distal end of the expandable element) to contain a mandrel, rod or similar component. The mandrel may be moveable and slidable axially along the axis of the catheter assembly and may extend the length of the inner lumen into and to the distal end of the inner lumen and the expandable element.
At the same time, however, the separate, concentric lumen structure of such a catheter shaft takes up additional space and requires a larger diameter catheter shaft to achieve a given degree of cross-sectional area for fluid flow to/from the expandable element. In addition, this design generally increases the size of the wrapped or folded expandable element because in these configurations the inner catheter lumen typically extends through the interior of the expandable element.
These and other deficiencies in and limitations of the above-described prior art approaches to treating bone deformities, such as vertebral body compression fractures, and other medical treatments involving inserting and inflating an expandable element through a narrow cannula are overcome in whole or in part with the systems, apparatus and methods of this invention.
Specific Invention Background—Standard IBT Devices and Procedures and their Limitations
As discussed above, surgical intervention at damaged or compromised bone sites has proven highly beneficial for patients, for example patients with back pain associated with vertebral damage.
Bones of the human skeletal system include mineralized tissue that can be generally categorized into two morphological groups: “cortical” bone and “cancellous” bone. Outer walls of all bones are composed of cortical bone, which has a dense, compact bone structure characterized by a microscopic porosity. Cancellous or “trabecular” bone forms the interior structure of bones. Cancellous bone is composed of a lattice of interconnected slender rods and plates known by the term “trabeculae.”
During certain bone-related procedures, cancellous bone is supplemented by an injection of a palliative (or curative) material employed to stabilize the trabeculae. For example, superior and inferior vertebrae in the spine can be beneficially stabilized by the injection of an appropriate, curable material (e.g., PMMA or other bone cement or bone curable material). In other procedures, percutaneous injection of stabilization material into vertebral compression fractures, by, for example, transpedicular or parapedicular approaches, has proven beneficial in relieving pain and stabilizing damaged bone sites. Such techniques are commonly referred to in this art as vertebroplasty. Other skeletal bones (e.g., the femur) can be treated in a similar fashion. Bone in general, and cancellous bone in particular, can be strengthened and stabilized by palliative insertion or injection of bone-compatible material.
Using vertebroplasty as a non-limiting example, a conventional technique for delivering the bone stabilizing material entails placing a cannula using an internal stylet into the targeted delivery site. The cannula and stylet are used in conjunction to pierce the cutaneous layers of a patient above the hard tissue to be supplemented, then to penetrate the hard cortical bone of the vertebra, and finally to traverse into the softer cancellous bone underlying the cortical bone. Once positioned in the cancellous bone, the stylet is then removed, leaving the cannula in the appropriate position for delivery of curable material to the trabecular space of the vertebra that in turn reinforces and solidifies the target site.
In some instances, an effectiveness of the procedure can be enhanced by forming a cavity or void within the cancellous bone, and then depositing the curable material in the cavity. The cavity can be formed in various manners (e.g., mechanical cutting or shearing of cancellous tissue, expansion of a balloon or other expandable device to compress cancellous bone and also cause a “height” of the bone to increase, etc.). To minimize the duration of the procedure and number of tools required, it is desirable to use the same cannula to first guide delivery of the cavity-forming device and subsequently to deliver the curable material. One such procedure entails initially locating a distal end of the access cannula immediately adjacent the target site. The cavity-forming device is then delivered through the cannula to the target site and operated to form the cavity. The cavity will have an enlarged width (e.g., diameter) as compared to a diameter of the cannula. The cavity-forming device is then removed from the cannula, and curable material can be delivered to the target site via the cannula.
To get the curable material to fill the cavity, the surgeon can either inject the curable material through the cannula and any intervening space (between the distal end of the cannula and the cavity) to reach the cavity or else push the cannula through the intervening space until the distal end is suitably located in the cavity before delivering the curable material. Under the first approach, curable material is deposited into the intervening space and may undesirably solidify or attach to the cannula. Further, the intervening space represents an uncontrolled volume that may negatively affect the surgeon's evaluation of whether a necessary volume has been delivered to the cavity. With the second approach, it may be difficult for the surgeon to accurately re-position the cannula within the cavity and/or may cause unintended damage to the tissue surrounding the cavity and/or to the cannula.
The access cannula is normally a metal tube rigidly defining a central axis. Conventional cavity forming devices typically include a longitudinally linear shaft carrying the expandable body. With this linear configuration, the shaft/expandable body progresses from the access cannula into the bone structure along a relatively straight or linear path that is coaxial with the access cannula's central axis. This linear configuration, however, may inhibit the surgeon's ability to form the cavity at a desired location. For example, with Kyphoplasty the confined nature of the inner vertebral body and surrounding anatomy may necessitate insertion of the access cannula immediately adjacent to one of the vertebra's pedicles. This access site, in combination with the linear configuration of the access cannula and the shaft carrying the expandable body, dictates that the expandable body can only be located in a relatively limited area in line with the access cannula's central axis. In some instances, this restricted spatial positioning of the expandable body relative to the desired target site may not be optimal.
The standard design of an Inflatable Balloon Tamp (IBT) device (presently available from many sources) used for vertebral bone dilatation/treatment procedures consists of an inflatable, relatively thick-walled, elastomeric balloon connected to the outer lumen of a concentric lumen catheter shaft which, in turn, is connected to a bifurcation assembly at the proximal end of the device. The bifurcation assembly consists of two arms, one of which arms connects to the outer concentric lumen of the catheter shaft and is used for supplying an inflation fluid to the balloon, while the other arm is axially aligned with the catheter shaft and connects to the inner lumen of the catheter shaft of the device. This conventional arrangement allows access to the balloon's interior through the outer lumen to allow inflation and deflation of the balloon, and it also allows access to the balloon interior through the inner lumen of the catheter shaft. The inner lumen of the catheter shaft generally holds a 0.035 inch diameter stainless steel mandrel. The mandrel typically can be positioned so as to extend for the length of the interior of the inner lumen, but it can also be fully removed from the inner catheter lumen at the proximal end of the device. The mandrel also typically has a male luer bonded on its proximal end to allow a secure connection of the mandrel assembly to the luer lock on the straight arm of the bifurcation fitting. Radiopaque marker bands are located inside the balloon along the exterior of the inner shaft and are used to mark the proximal and distal ends of the balloon to assist the physician in positioning the balloon under fluoroscopy prior to inflation of the balloon.
The conventional IBT device is delivered to the vertebral body of a patient by means of a needle cannula. The standard for use in such procedures was originally a standard wall 8-gauge (0.135 inch or 3.4 mm inside diameter) needle together with a suitably sized IBT instrument. A smaller, thin-walled 10-gauge (0.114 inch or 2.89 mm inside diameter) needle was later introduced and has since gained favor because of its smaller size, which makes a smaller opening in the patient, and which in turn creates less trauma and aids in a quicker recovery time for the patient. The smaller size opening created with the 10-gauge needle also reduces the chances of fracture of the pedicle and provides the ability to treat smaller vertebrae that might not be able to accommodate an 8-gauge needle. In the bone dilatation form of a vertebral treatment procedure that uses an expandable element, an IBT device sized to accommodate the inner diameter of the cannula is introduced into the interior of the vertebral body of a patient. The expandable element of the device is then inflated inside the fractured vertebra. For a compression fracture, the procedure is intended to substantially restore the bone to its pre-fractured dimensions and, on withdrawal of the balloon, the space created by the inflated balloon can be filled with bone cement that hardens in place to stabilize the fracture.
A second, alternative form of a vertebral treatment procedure (one that is generally known in this art as “vertebroplasty”), however, can be performed without the use of an IBT device and without an expandable element. This alternative “vertebroplasty” procedure presently uses a standard eleven (11) gauge (0.094 inch or 2.4 mm inside diameter) needle cannula. But, rather than using an IBT device to first create a cavity to restore the vertebrae dimensions, in this alternative procedure the cement is injected directly into the vertebral body to stabilize the fracture. The medical decision about which of the two procedures should be performed in a particular case is best decided after the physician has fluoroscopically assessed the condition of the patient's vertebra.
The ability of a physician to decide between the two procedures at or shortly after the start of a procedure is currently limited, however, by the size of the opening into the bone interior. If the opening was created using an 11-gauge needle in anticipation of performing a vertebroplasty (no balloon element) procedure, that opening will not accommodate a cannula that is large enough to pass a conventional 10-gauge IBT assembly if the physician decides instead on the bone dilatation procedure. Accordingly, it would be highly desirable to have an IBT catheter assembly (including a conforming expandable element meeting current medical protocols) that is capable of fitting through the smaller interior opening of an 11-gauge needle cannula. This would allow the physician to start a procedure with a smaller entry opening in the skin and bone, use an 11-gauge cannula, and then still be able to select either type of bone treatment procedure, depending on which procedure is deemed best suited to the patient's condition. The ability to use an 11-gauge cannula in such procedures also would substantially reduce the chance of fracturing the pedicle (because a much reduced area of the pedicle would need to be opened to accommodate the smaller cannula), and it would also allow for the treatment of smaller vertebra as described above.
Accordingly, there is a currently unfilled need in this art for a system, apparatus and method wherein a narrow gauge (e.g., an 11-gauge) cannula can be utilized in combination with a specially designed catheter/expandable element apparatus adapted and sized to slide through the interior of the associated narrow gauge (e.g., an 11-gauge) cannula.